A perovskite titanium-containing composite oxide represented by barium titanate is widely used for functional materials such as a dielectric material, a laminated ceramic capacitor, a piezoelectric material, and a memory. In recent years, in line with the trend toward small-size, light-weight electronic devices, it has been desired to develop a method for obtaining a perovskite titanium-containing composite oxide particle with a smaller particle size and more noticeable dispersion properties at low cost. Further, such a titanium-containing composite oxide particle that has the above-mentioned characteristics is expected to be applied to a photocatalyst.
The perovskite titanium-containing composite oxide is obtained by a solidus method of mixing finely-divided particles of the raw materials such as an oxide and a carbonate in a ball mill, and carrying out the reaction at a high temperature of over about 800° C.; by an oxalate method of first preparing a composite salt of oxalic acid, followed by thermal decomposition; by an alkoxide method of subjecting a raw material such as a metal alkoxide to hydrolysis to obtain a precursor; or by a hydrothermal synthesis method of allowing the raw materials to react at high temperature under high pressure to obtain a precursor. In addition to the above, the perovskite titanium-containing composite oxide can be also obtained by a method of preparing titanium oxide or the precursor thereof, dispersing the titanium oxide or precursor thereof in a solvent, and making a composite of titanium oxide or precursor thereof in the solution by the addition of a predetermined element (Japanese Laid-Open Patent Application 8-119633), and a method of employing titanium tetrachloride or titanium sulfate as the raw material (Japanese Laid-Open Patent Application 59-39726).
However, the solidus method produces particles with a large particle size, lacking uniformity, which are not suitable for the functional materials such as the dielectric material and piezoelectric material although the low manufacturing cost is industrially advantageous. The particle size obtained by the oxalate method is 0.2 to 0.5 μm, which is smaller than that by the solidus method, but not sufficiently small. The alkoxide method can produce particles with a particle size of 20 nm to 30 nm, but the manufacturing cost is high because organic materials are used as the raw materials. In addition, the hydrothermal synthesis method has a problem in that the cost becomes high because special facilities are required to carry out the synthesis under conditions of high temperature and high pressure.
Unless the dispersion properties of the particles are sufficient, the particles will aggregate in a solvent even if they can be prepared with a small particle size by any of the above-mentioned methods. The result is that when the particles are molded and sintered to prepare a product of the functional material such as a dielectric material or piezoelectric material, the particles cannot exhibit satisfactory characteristics. Furthermore, of the perovskite titanium-containing composite oxide particles, SrTiO3 is particularly expected because of its photocatalytic activation performance. However, to obtain small particles is not easy. Namely, it is hard to inexpensively obtain particles with excellent photocatalytic activation performance.
The object of the present invention is to provide a perovskite titanium-containing composite oxide particle with a small particle size and excellent dispersion properties, and a sol thereof at low cost.